In pot spinning, in particular with so-called single stage pot spinning, the rewinding process of the spinning cake deposited on the inner centrifuge wall of the pot spinning unit is customarily initiated by means of a rewinding tube, i.e. an empty tube, which is kept in readiness during the regular spinning process on the yarn guide tube and is lowered over the mouth of the yarn guide tube for initiating the rewinding process. In the process, the edge of the empty rewinding tube grasps the rotating yarn leg exiting from the yarn guide tube, with the result that the spinning cake deposited on the inner wall of the centrifuge then rewinds onto the empty tube.
However, difficulties arise if a yarn break occurs during the spinning process, i.e. during the build-up of the spinning cake. Although with single stage pot spinning it is possible to continue spinning after a yarn break, during subsequent rewinding the amount of yarn spun up to the time of the yarn break remains in the spinning centrifuge and as a rule can only be removed by stopping the centrifuge.
Various methods and devices have already been developed in the past which were intended to make it possible to still rewind the spinning cake deposited in the centrifuge after a yarn break and in this way to save the yarn for further processing. However, most of the known methods and devices have various disadvantages and therefore were not accepted in actual use.
For example, a method is known from German Patent Publication DE 44 00 999 A1, which had been developed in connection with the so-called dual-stage pot spinning. In case of a yarn break, a firm catch yarn is introduced into the rotating spinning centrifuge through the yarn guide tube with this method. The catch yarn becomes twisted together with the inner winding of the spinning cake, so that the rewinding process, i.e. the second stage of the known pot spinning method, can be initiated thereafter by pulling the catch yarn back. However, the use of a firm catch yarn is disadvantageous in this method, since the foreign yarn must afterwards be carefully removed. Furthermore, the functional dependability of this method is relatively low.
A special tube is described in German Patent Publication DE 195 23 937 A1, which has a radially projecting plate-like widening at one of its longitudinal ends. After a yarn break, the broken yarn end as a rule lies against the inner surface of the spinning cake in the form of a chord-like extent of the yarn. The plate-like widening of the specially designed tube is intended to grasp this chord-like yarn end portion and to use the latter for initiating the rewinding process. However, in actual use this special rewinding tube was not convincing in connection with all yarn types. The chord-like yarn end portion sometimes is not clearly defined so that grasping this yarn portion was shown to be extremely difficult with some yarn types.
Devices for initiating the rewinding process after a yarn break in connection with pot spinning devices are also known from Swiss Patent 348 346 and German Patent 842 916. The Swiss patent describes by way of example a broom-like tool which is manually introduced into the rotating spinning centrifuge after a yarn break and has thin wire feelers for placement against the inner layer of the spinning cake to initiate the rewinding process. Because of the high rpm of modem spinning centrifuges, the manual insertion of such a tool into the spinning centrifuge represents a considerable risk of accidents and is therefore no longer permitted for use in present-day spinning machines, if for no other reason than protection against accidents.
German Patent 842 916 describes a device having an arm which can be introduced into the spinning centrifuge and placed against the inner yarn windings of the spinning cake. However, with this device it is disadvantageous that the detaching tool, i.e. the arm placed against the spinning cake, is also wound during the rewinding process. As a rule, the spinning cop created in the process can no longer be unwound and therefore constitutes waste.